Abstract
The surface morphology of polystyrene thin films formed from various molecular weight polystyrene and solvent conditions is studied. When spin-cast from tetrahydrofuran (THF) wrinkles are formed at the extremities that have periodicity with wavelengths in the μm range and amplitudes in the nm range but varies with molecular weight. A mixed solvent system consisting of THF and dimethylformamide (DMF) leads to periodic structures only with THF-rich compositions. THF and DMF have similar properties relevant to spin-casting: density, surface tension, molecular weight, and viscosity but different boiling points and room temperature vapor pressures, demonstrating that formation periodicity requires a volatile solvent. The formation of the surface structures is attributed to the Marangoni effect and the film thicknesses and wave parameters are shown to be consistent with literature models.
Highlights
In the present state of materials science, where there is a push for devices to be made smaller, it is important to understand a material’s physical and chemical properties from both the perspective of the surface and the bulk
We find that a high evaporation rate is required to obtain a periodic surface morphology while a low evaporation rate leads to a random surface structure
Materials Science where o is the initial viscosity of the solution, opol is the mass fraction of polymer in the initial solution, sol is the mass fraction of the solvent in the gas phase at equilibrium, g is the kinematic velocity of the overlying gas, c is a constant that depends upon the Schmidt constant, Dg is the diffusivity of the overlying gas, is the density of the solution, psol is the vapor pressure of the solvent, Msol is the molecular weight of the solvent, R and T represent the ideal gas constant and absolute temperature, and is the angular speed
Summary
In the present state of materials science, where there is a push for devices to be made smaller, it is important to understand a material’s physical and chemical properties from both the perspective of the surface and the bulk. A defining feature of an interface is the surface morphology, which is a broad term and can be considered on many different scales. In modern thin film systems one must consider the nano/micrometer regions of surface morphology as well as the macro features. The push for understanding and controlling surface morphologies historically arises from the field of adhesion [9,10], but certain patterning in materials has been shown to be promising for use in photonic devices [11,12,13,14,15,16,17,18,19,20], stretchable microelectronics [21,22], mechanically switchable wetting [23], and microfluidics [24,25]. A rigid skin layer is transferred onto the elastomer and the strain is released, which causes buckling of the skin layer and produces wrinkles, creases, or folds
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
